There is a general desire to increase the number of communication channels supported by telecommunications equipment, for example telephony switches, to support the growing needs of the telecommunications industry and its users alike.
A Line Interface Unit (LIU) is used in telecommunications equipment to transmit information over communication lines and to retrieve information that is transmitted over communications lines. The transmit side of an LIU converts a digital signal into the correct analogue waveform for transmission. The receive side of an LIU adapts to the amplitude of incoming signals and recovers first the associated clock then the transmitted data. Different LIUs support different numbers of channels; some support just a single channel and others support sixteen or more channels. An isolation transformer is provided for each channel so that the LIU is galvanically isolated from the incoming signal lines. There are also protection components which protect the LIU against surges and other high voltage events on signal lines.
Some systems provide two (or more) mounting boards in the equipment chassis, each with LIUs and isolation transformers in a failover arrangement, whereby the system can fail from one mounting board to the other. Such systems are limited in terms of the channel density that they can achieve. This is because the addition of required components would necessitate increasing the size of the chassis in which they are provided or modifying the chassis in some other way, which may not be desirable.
It would be therefore be desirable to provide telecommunications equipment with the potential for increased communication channel density whilst ameliorating the need to modify or increase the size of a housing.